How does hair conditioner work?

You’ve lathered. Rinsed. Repeated. Now, it’s time to condition. With steam rising, you massage the slippery, sweet-smelling conditioner onto your hair, and in the three to five minutes it takes to work, you may find yourself asking, “How exactly does this stuff transform my hair into a stockpile of silkiness?”

The answer is that a certain opposites-attract chemistry is going on between your hair and your conditioner.

Every day, your cascading locks weather a series of storms. One day it might be a run-in with a flat iron, another could bring vicious winds from a blow dryer. The result: hair – once shiny and smooth – is now frizzy, clumped and yearning for repair.

To understand the chemical romance that starts the moment you “generously spread the conditioner from root to tip” (as the bottle instructs us), you have to understand the structure of hair.

Under the microscope, hair strands are flaky-looking. These “flakes” are dead skin cells overlapping to form a cuticle layer that protects the fragile inner layers of a hair strand. Light reflects off this cuticle layer, giving hair its natural shine. The average person has between 120,000-150,000 hair strands and they look their best when the overlying cuticle flakes lay tightly against one another. When hair begins to look frizzy or limp, it means the cuticle layer is being worn down and the overlapping cells are no longer lying snugly flat.

“Imagine frayed rope,” says Robert Lochhead, a polymer scientist at the University of Southern Mississippi in Hattiesburg. Lochhead is also a consultant for several companies that make cosmetic and personal care products. He explains that on a molecular level, the invisible bonds that hold the cuticle cells together weaken over time. Cells become more and more loose and snag against cuticle flakes of other strands. The individual hair strands then tangle and sometimes break off. This change in the way our hair looks and feels is often the first reminder that it may be time to reach for the conditioner.

Hair conditioner is made of only a few ingredients but it’s the cationic surfactants that do most of the work. At one end of every cationic surfactant molecule is a positive charge that binds to the negative charge of a hair strand. The attraction is so strong that the surfactants completely surround the strand and cover the cuticle flakes, like a customized hair envelope. The small amount of acid in the conditioner makes the cuticle flakes fall tightly against each other and hair feels smooth again, even after you rinse the conditioner out.

If you’re a fan of the two-in-one conditioning shampoos, your desire to be efficient is an opportunity for even more science atop your head.

Lochhead is a pioneer in this arena. In fact, the concept of washing and conditioning your hair at the same time is called the “Lochhead Effect.” In a two-in-one product, he explains, the catatonic surfactants remain suspended in all the suds while the shampoo is working to break down oils and dirt. Then, when you rinse the shampoo out, the surfactants are “triggered” by the water to bind to the hair, while only the dirt and oil washes away.  Surfactants can also convey other cuticle-protecting substances, such as silicone, to the hair.

“When you think of silicone, think of oil droplets in water,” explains Ali Dhinojwala, a chemist at the University of Akron who is trying to figure out optimal ways of delivering silicone to hair. “A lot is actually lost during rinsing. It’s hit and miss, and that is what we are trying to figure out.” He says that the solution right now is to add a lot of silicone so that a fair amount will bind to the hair.

Call it a bit of shower-time chemistry. Whether you carry two bottles into the shower, or prefer a two-in-one kind of deal, the science is at your fingertips.